In the following code You find all to solve the problem:
1. a row generator do build up a list of data for a month (here actual month)
and
2. the function to get the names for the (english) days
So You have to count the wanted days and adapt it to Your problem
Good luck

And if you don't want to use a brute force computing, you can think that the number of Sunday (or any other one) in a month is 4 or 5.
For Sunday, it is 5 only if first day is Sunday, Saturday or Friday and number of days in month is greater than or equal, respectively, 29, 30 or 31.
I let you write this in SQL.

Yes, I know, this is a mined query, I let it as it to see if someone will see the limits of the query.
And yes, it only works for territories that have Sunday as first day of the week (which is not the case of France ).
Now I let OP generalizes the query to any territory.
By the way, his country has the advantage to be the easiest case with a week starting on Friday.